To find the volume of the object made of four rectangular prisms, we first calculate the volume of one prism.
The formula for the volume \( V \) of a rectangular prism is: \[ V = \text{length} \times \text{width} \times \text{height} \]
Given the dimensions:
- Length = 75 cm
- Width = 30 cm
- Height = 20 cm
We can calculate the volume of one prism: \[ V = 75 , \text{cm} \times 30 , \text{cm} \times 20 , \text{cm} \] First, calculate \( 75 \times 30 \): \[ 75 \times 30 = 2250 , \text{cm}^2 \]
Next, multiply by 20 cm: \[ 2250 , \text{cm}^2 \times 20 , \text{cm} = 45000 , \text{cm}^3 \]
So, the volume of one rectangular prism is \( 45000 , \text{cm}^3 \).
Since the object is made of four such prisms, the total volume of the object is: \[ 4 \times 45000 , \text{cm}^3 = 180000 , \text{cm}^3 \]
Therefore, the volume of the object is \( \boxed{180000 , \text{cm}^3} \).